All boat owners are concerned about leaks below the waterline. However that attitude is not as strict when it comes to leaks topside even though it’s no fun trying to sleep on the boat in a rainstorm as water leaks in around a port and gets your bedding wet. Instead of finding and correcting those minor leaks that allow only nuisance amounts of water in when it rains, we cover them up with a tarp (or tape). Those minor leaks, often treated as only a nuisance, can cause serious problems. Leaks around deck fittings can saturate the core and cause serious structural problems as bulkheads and interior wood begin to rot. Wet cores and rotted bulkheads can be repaired or replaced but those are major jobs that you shouldn’t have to do and won’t if you take prompt action to fix the leak and not just patch it.
Fittings that show any sign of leaking should be removed and rebedded. A smear of silicone seal around the fitting just won’t do it. Remove the affected fitting, remove all the old sealant and replace the fitting with new sealant. To prevent those smears of sealant “squeeze-out”,
(1) put masking tape over the area where the fitting goes then install it dry temporarily. With a utility knife cut the tape around the base of the fitting.
(2) Remove the fitting and pull up the tape that you have cut out. Reinstall with sealant and tighten snugly.
(3) Allow the sealant to set up overnight, retighten the fasteners and clean up excess sealant and remove tape.
If you have wiring exiting the base of the mast, you should make sure the wire has a “drip loop” to keep rainwater from running on down into the bulkhead fitting.
If you are installing fasteners through a cored deck, you can seal the core by
(1) removing the core around the hole
(2) filling the hole with epoxy filler, with tape on the bottom
(3) redrilling the hole for the fastener.
You can use a bent nail or a large roofing nail with a notch in the head in an electric drill to remove the core around a hole. Holes with this treatment not only seal water away from the core the also add structurally to the fitting attachment. This may seem overkill but this technique makes for a solid, leak free installation.
It’s a bit time consuming, but not difficult.